The present invention relates to an apparatus for observing and examining lens opacity in human eyes, and more particularly to a retroillumination image photographing apparatus which is capable of obtaining a useful image of the lens.
A retroillumination image photographing apparatus in which an eye to be examined is projected to a light and the crystalline lens is retroilluminated with reflection at the fundus, thereby enabling it to observe the state of opacity in the crystalline lens has been heretofore well known.
In such a conventional retroillumination image photographing apparatus, alignment is performed by moving the apparatus main body in a longitudinal direction so as to photograph a position where an opacity area appears most clearly when the lens opacity is photographed.
With a conventional apparatus, however, it has not been possible to know exactly how deep the photographing position exists in the crystalline lens.
As a result, it has not been unable to photograph always at the same depth even for the same patient, which has interfered with the follow-up of chronological change in the progress of a cataract. Namely, there has been such a problem that pertinent evaluation cannot be made unless an error of the position of a photographed crystalline lens is taken into consideration when an opacity area is obtained repeatedly from the retroillumination image, thus being impossible to grasp a delicate change.
Further, the opacity areas are different depending on the types of cataract, and pertinent diagnosis such as on either nuclear cataract or cortical cataract (an opacity area exists in the cortex on the side of an iris or a vitreous body) could not be made.
Furthermore, it has not been possible to know the extent of opacity exactly even if a photograph is performed while changing the depth position.